Similar to spyware, adware is a slightly less threatening type of program that usually displays unwanted pop-up ads while you use your computer. Installed without your knowledge, adware can allow companies to moniter your browsing patterns. Pop-up ads that are displayed while you are using your computer are usually directed based on your surfing habits. One of the most threatening aspects of adware is that it is possible for an adware program to download files to your computer by saying that the dowload is necessary for some reason, or possibly without notifying you at all.